The present Applicant has described previously how a pagewidth inkjet printhead may be constructed from a plurality of abutting printhead integrated circuits (also known as printhead ICs, printhead chips and printhead dies). As described extensively in, for example, Applicant's U.S. application Ser. No. 11/014,732 filed on Dec. 12, 2004 (the contents of which is herein incorporated by reference), a pagewidth printhead usually comprises a plurality of abutting printhead ICs attached to a liquid crystal polymer (LCP) ink manifold via an adhesive intermediary layer, which is sandwiched between the LCP ink manifold and the printhead ICs. The adhesive intermediary layer is typically a laser-drilled epoxy-coated polymer film.
The construction of such printheads presents a number of design challenges. Firstly, the printhead ICs must be mounted with high precision on the polymer film so that laser-drilled holes in the film are aligned with backside ink supply channels in the printhead ICs. Secondly, the MEMS fabrication process for the printhead ICs should preferably present the ICs in such a way that facilitates bonding onto the intermediary layer.
Hitherto, the Applicant has described how backside MEMS processing of a printhead wafer may be performed to provide individual printhead ICs (see, for example, U.S. Pat. No. 6,846,692, the contents of which is incorporated herein by reference). During backside MEMS processing, the backside of the wafer is ground to a desired wafer thickness (typically 100 to 300 microns) and ink supply channels are etched from a backside of the wafer so as to form a fluidic connection between the backside, which receives ink, and nozzle assemblies on a frontside of the wafer. In addition, backside MEMS processing defines dicing streets in the wafer so that the wafer can be separated into the individual printhead ICs. Finally, any photoresist in the wafer is ashed off using an oxidative plasma. The exact ordering of backside MEMS processing steps may be varied, although backside MEMS processing is typically performed after completion of all frontside MEMS fabrication steps, in which the nozzle assemblies are constructed on the frontside of the wafer.
In the process described in U.S. Pat. No. 6,846,692, the individual printhead ICs end up mounted, via their backsides, to a handling means. The handling means may be a glass handle wafer, with the printhead ICs attached thereto via a releasable adhesive tape e.g. UV-release tape or thermal-release tape. Alternatively, the handling means may be a wafer film frame, with the printhead ICs being attached to a dicing tape supported by the wafer film frame. Wafer film frame arrangements will be well known to the person skilled in the art.
The printhead ICs may be picked off individually from the handling means (for, example, using a robot) and either packaged or bonded directly to an intermediary substrate to construct a printhead. U.S. Pat. No. 6,946,692 describes how a vacuum pick-up may be used in combination with a reciprocating x-y wafer stage and a UV lamp/mask to remove individual printhead ICs from a glass handle wafer.
However, a problem with the process described in U.S. Pat. No. 6,846,692 is that the individual printhead ICs must be removed from the handling means and then aligned and bonded with high accuracy to the intermediary substrate. Whilst robot handling of the ICs helps to improve alignment accuracies, there are inevitable alignment losses in such a process.
It would be desirable to provide a process for removing MEMS devices, such as printhead ICs, from a handling means, which facilitates alignment of the devices when bonded to a further substrate, such the intermediary substrate described above.
It would be further desirable to provide a process for printhead construction, which facilitates the use of alternative non-polymeric intermediary substrates. Polymeric adhesive layers are inexpensive and convenient to handle, but suffer from comparatively high thermal expansion relative to the silicon printhead ICs and the LCP ink supply manifold. A comparatively high coefficient of thermal expansion for the intermediary substrate exacerbates alignment problems during construction and may even lead to loss of alignment over the duration of the printhead lifetime.